Starrag Machining Centres Are A Cut Above

Andrew Churchill is out to break the mould of gas turbine blade manufacture by using his battery of Starrag high-speed five-axis machining centres to machine blades complete from solid billet in a single set-up, rather than machining large batches of forgings to size.

The process route offers a number of advantages over the traditional route of blade production:

Machining from billet negates the need for relatively large batch sizes – one-offs to 90-off are feasible compared to a minimum batch of, say, 300-off when forgings are used;

The resulting time savings can be enormous – lead times for forgings can be extensive, sometimes taking a year from ordering the die to the delivery of forgings - while production from billet has a lead time of just a few weeks’;

The argument that blade integrity from billet is weaker than a forging is being dispelled by exhaustive fatigue and stress testing; and, most importantly

A blade that is milled from solid can be held to far tighter tolerances than a forged blade, according to Mr Churchill. ‘And ultimately better tolerances means the engine runs more efficiently and cleanly, better and therefore far more economically,’ he asserts.

Mr Churchill continues: ‘We are already proving the cost-effectiveness of the process at both the blade design/development stage and in the ‘legacy’ manufacture of spares/replacement blades in current typical batch sizes of 80/90-off, and it’s only a matter of time before the viability of machining from solid or over-size forgings challenges precision forgings in volume production on a cost per part basis,’ says the managing director of precision engineers, JJ Churchill.

The route to achieving such a highly flexible method of blade production was mapped out by the Market Bosworth (Midlands) company around six years ago, when it started its investment in Starrag high-speed five-axis blade production machining centres.

That said, JJ Churchill has been involved in compressor blade machining since 1947 for Rolls-Royce (turbine blade production being added more recently), when company founder Walter Churchill (Andrew Churchill’s grandfather) worked with Air Commodore Sir Frank Whittle, who is accredited with the invention of the turbojet engine.

Today, a company speciality is the prototype development and spares supply on a variety of aircraft programmes, including developmental blades for the Airbus A350 Trent engine and F35 Joint Strike Fighter through to Industrial Rolls-Royce RB211 kitted production volumes and legacy demand for the Tornado RB199.

JJ Churchill continues to develop its expertise in the principal markets of aerospace, defence, industrial and power generation and is a first-tier supplier to OEMs such as Rolls-Royce, BAE Systems, Cummins, Perkins, Siemens and Alstom - developing, testing and assembling as a preferred supplier to these organisations on long-term projects.

Today, with 120 employees and a turnover of £20 million, Mr Churchill – who joined the family company 11 years ago after a career abroad including in Australia, China and Hong Kong with Burmah Castrol - says his plan to achieve a £50 million turnover by 2019 rests substantially with his Swiss-manufactured Starrag machining centres, supplied by Birmingham-based Starrag UK.

Blade work via these machines currently accounts for 25 per cent of business but by utilising the machines’ impressive capabilities, the intention is to ‘prove without doubt’ the viability of the milled aerofoil approach to higher volume production.

‘While we continue to successfully undertake both development and legacy work for blue chip clients, I could see that if we stayed the same we wouldn’t grow,’ says Mr Churchill. ‘Yes, we would continue to earn a relatively good living – for example, Rolls-Royce has never declined a spares order for any engine it has ever made. But I’m not interested in ‘lifetsyle manufacturing’ and it was clear that the market was changing, with fewer suppliers attracting a greater amount of work.’

Highlighting that a main benefit of being a family-owned SME is the ability for quick decision-making – ‘the larger companies eventually ‘get there’ but small firms are ‘nimble’ and can be quicker off the mark’, Mr Churchill decided to take the plunge and in 2008 (a recessionary year when the company’s turnover halved) he doubled JJ Churchill’s capital investment and installed the first Starrag, a model SX 051B (the predecessor to the current LX 051).

‘The adage of ‘if you stand still, you will disappear’ rings true,’ he continues. ‘But to invest in this way during recession we had to ensure we had a robust strategy; we needed to be certain that our targets were realistic. We decided to investigate machines and machining methods that would transform our approach to blade production. We needed to be better (right first time), faster and lower cost (through reduced cycle times) than anyone else – including the OEMs themselves – and we are well on our way to achieving this with the advanced blade technology strategies of the Starrag machines.’

After travelling the world – specifically Japan, Germany and Switzerland – investigating machines for simultaneous five-axis machining, Mr Churchill says ‘it was clear that the Starrags are one of the very few that have been designed and developed specifically for blade manufacture’.

‘They are very complex machines, but everything about them is designed for the purpose of machining gas turbine blades, with seamlessly integrated Starrag machining strategies and powerful Siemens software, plus the service support from highly-skilled UK-based engineers. Combined, these features put the machines streets ahead of everything else,’ he says.

‘I’m interested in the cost of the blade, not the cost of the machine,’ he asserts, and the proof was in the pudding: a recent development blade aerofoil was machined in just 90 minutes in titanium compared to nine hours on a bespoke solution – and the blade machining demonstrated a staggeringly high Cpk process capability.

The company’s first order was for gas turbine blades for power generation, machined from nimonic 105, for Siemens. ‘Siemens saw that we had a Starrag and knew we were serious,’ affirms Mr Churchill, who adds that his company’s work in this field has since expanded into industrial gas turbine stators and rotors as well as variable vanes.

The Starrag blade centres incorporate rotary and gantry coupling variations that are integrated into an innovative linear axis design that dissipates tension and thermal expansion. Machining accuracy is further assured by the fact that the B axis locate the tools’ pivotal point in the centre of all axes.

Mr Churchill continues: ‘Once we had proven the technology, we didn’t hesitate to continue to invest in Starrag blade centres,’ and four more models followed over the years, including the larger capacity LX151 and three LX 051 models that between them offer machining capacities up to 700 mm long by 400 mm diameter and spindle speeds to 18,000 revs/min.

A key to the success of these machines at JJ Churchill is the use of the RCS CAM software (three seats are in use) which has been developed by Starrag specifically for five-axis high-speed blade machining.

With extended selection of machining strategies, RCS provides highly efficient and effective programming due to its parametric input structure, and cycle times are minimised via the software’s optimal selection of milling strategies.

RCS is used by JJ Churchill in conjunction with Unigraphics CAD and all machining programs are transmitted to the machines via DNC link.

In addition to creating difficult features such as variable fillet radii (now a feature of the latest RCS software), JJ Churchill has also developed an in-process ‘polishing’ routine for the Starrags, where clever fixturing to an unrivalled +/- five microns is used for holding blades, working in conjunction with traditional encapsulation techniques for complete blade machining. All fixturing is produced in a highly skilled in-house toolroom, a result of when the company used to be involved in the manufacture of tooling and tool holders.

Carbide tooling predominates and there is no preferred tooling supplier – ‘we use whatever is best’ - and the machines run seven days a week across three shifts. The usual practice is to stagger set-up/machining to enable one operator to manage multiple machines.

Blades are rough milled to within 2-3 mm of final form before finish machining, and the Starrags’ ‘super finish mode’ can see blades finished to typically 0.7/0.8 Ra. Every blade is 100 per cent inspected on Mitutoyo co-ordinate measuring machines – there are four such CMMs in the bar-blade cell and these utilise powerful software (the same as used by Rolls-Royce) to generate a variety of data, including SPC, as required.

Coupled with a host of quality standards and accreditations such as SC21, JJ Churchill’s use of Starrag blade machining centre technology has earned it several supplier awards in recent years, including being Rolls-Royce Global Aerospace Supplier of the Year and the Cummins Supplier Award for Europe, Middle East and Africa Regions, both awarded in 2010.

‘Starrag’s machining technology has created a material shift in what’s possible in gas turbine blade manufacture,’ concludes Mr Churchill. ‘With the appropriate technology, investment and software, coupled with suitable staff training which includes apprenticeships that are targeted to increase from 6 to 10 per cent of the workforce – you need to have the best people in the world to operate the best machines in the world – we know we can meet every expectation,’ he says.